The proposed research program is a general, comparitive investigation of the neurophysiological basis of circadian rhythms in three diverse organisms - rogents, crayfish, and cockroaches. 1. Rodents: In rodents we plan to investigate the role of the suprachiasmatic nucleas and associated CNS structures in the generation of circadian rhythms of locomotor activity and brain temperature utilizing partial and complete lesions of the SCN as well as local administration of pharmacological agents via cannuli. We hope to confirm the suggestion that this nucleus constitutes an autonomous "biological clock" and to examine the functional and anatomical sub-structure of this putative circadian pacemaker within the SCN. 2. Crayfish: A circadian rhythm in multiunit activity of the second root of the sixth abdominal ganglion has been demonstrated in the crayfish abdominal nerve cord isolated in culture. Experiments are proposed to determine whether or not the surgically isolated nerve cord can be entrained in vivo and in vitro, and if so, to identify the necessary photoreceptor. We will also attempt, with the use of electrolytic lesions, to localize the pacemaker(s) involved in generating the rhythm. 3. Cockroaches: In the cockroach we plan to continue experiments in which surgical and electrolytic lesions are utilized to identify neuronal pathways and regions of synaptic connection which mediate interactions between the bilaterally paired components of the circadian system controlling locomotor activity. We also propose to investigate the phenomenon of temperature "entrainment" of cockroaches in which the optic lobes have been ablated. The immediate goal of these studies is to demonstrate that temperature cycles entrain an oscillator rather than simply impose rhythmicity, and to determine which regions of the CNS are involved. BIBLIOGRAPHIC REFERENCES: Daan, S., D. Damassa, C.S. Pittendrigh, and E. Smith. An Effect of Castration on Testosterone Replacement on a Circadian Pacemaker in Mice (Mus musculus). PNAS 72:3744-3747, 1975. Pittendrigh, C.S. and S. Daan. A functional analysis of circadian pacemakers in nocturnal rodents. I. The stability and lability of spontaneous frequency. Jr. Comp. Physiol.